A trial atomization is performed on the trial platform. After the appropriate supply of heat within the heat duct, through the irradiation of electromagnetic waves of determined frequency into the heat duct these waves are absorbed by the atomized trial and a resulting absorption spectrum is registered, which is characteristic for the respective trial. The corresponding absorption spectrum is determined by the atom absorption spectrometer.
The trial platform has a certain effective volume, into which the corresponding trial can be inserted by means of a pipette or the like. At its free ends, the basically basin-shaped trial platform is generally equipped with partially circular rims, which restrict the effective volume in a lateral direction.
Trial platforms in common use heretofore have proved, at relatively high temperatures and especially under the impact of strongly oxidizing reagents, to lose their shape and to give way against an inside wall of the heat duct. This increases the contact surface between the trial platform and the heat duct, resulting in such a strong heating of the trial platform by the introduction of heat from the heat duct that there is no longer an optimal temperature delay relative to the heat duct. Such a temperature delay, however, is desirable in order to improve and stabilize the atomization conditions for the elements to be determined, also in respect to continuing high increments of heat at high temperature.
It should also be mentioned that, even with a minor loss of shape of the trial platform, the measurements are no longer reproducible. For all these reasons the trial platform must be replaced if there is a corresponding loss of shape. This is relatively difficult and, in some cases, in addition to the trial platform the heat duct at least must also be replaced, resulting in increased costs.
The invention therefore aims to make ongoing improvements in a furnace of the aforementioned type, so that the trial platform has an increased lifetime along with high reproducibility of measurements and simple operation as well as low costs.
According to a preferred embodiment of the invention, this task is fulfilled in that the trial platform has a geometric structure stabilization device, which reduces the ratio of the effective volume of the trial platform to the rim volume. In the invention disclosure, the rim volume refers to a volume occupied by the rims of the trial platform.
The structure stabilization device prevents the trial platform from prematurely losing its shape and keeps the contact surfaces between the trial platform and the heat duct from increasing. As a result, on the one hand, the lifetime of the trial platform is increased. An increased lifetime also leads to a cost reduction in operating the furnace. In addition, the stabilized structure of the trial platform results in a good reproducibility of the measurements carried out with the trial platform. Another result of the stabilized structure is that even aggressive media can be injected into it better and with increased lifetime of the trial platform and can be measured by means of an atomic absorption spectrometer.
It is true that the effective volume of the trial platform is to some extent reduced by the structure stabilization device. This reduction, however, is relatively slight, so that sufficient trial material can be injected even with the inventive trial platform. In addition, the trial platform of this invention can be larger than a known trial platform while retaining the same amount of space in the heat duct, and thus the effective volumes of the inventive trial platform and of the known trial platform are essentially equal.
The inventive trial platform can be used particularly in a heated graphite atomizer (HGA). This is also true for transversally heated graphite atomizers (THGA).
To ensure that the trial platform is easy to operate and that it can fit in the heat duct, it can be integrated into the heat duct. The integration is normally ensured by means of a basically punctiform connection with the heat duct. In the remaining area no direct contact should exist between the trial platform and the heat duct, in order to minimize any heating through the addition of heat between the tube and the platform.
Such an integrated trial platform is generally of small mass and has a relatively large surface. In the case of one trial platform in common use, its length for example is 10 mm, the thickness of the rim is 0.47 mm, and the corresponding height of the rim is 0.08 mm. Because of the small mass and the great surface, the trial platform can be heated up quickly by heat rays emitted from the heat duct. The punctiform connection with the heat duct results in an optimal temperature delay with respect to the tube, a very desirable characteristic for a trial platform with stabilized temperature.
A trial platform that can be produced simply and relatively economically, which contains little uncleanliness, and which is relatively easy to operate can be formed of graphite as its base material. A surface coating is generally applied to this base material pyrolytically. The surface coating increases the chemical stability of the platform.
In order to maintain the known advantages of existing trial platforms in the inventive trial platform without having to use other materials, additional materials, additional structural elements or the like, the invention proposes the geometrical structure stabilization device. This installation can, for instance, be configured through a reduction of the platform length. The corresponding length reduction in comparison to the existing trial platforms results, in simple manner, in a stabilization of the trial platform, considerably prolonging its effective life; that is, the shape of the trial platform is stable for a longer period.
Such a length reduction and other minor modifications in the geometry of the trial platform can lead to a smaller effective volume. This is tolerable, however, since the effective volume of the inventive trial platform remains well suited for receiving a sufficient trial quantity for carrying out corresponding measurements.
It was observed that the platform length could be reduced by 10 to 40 percent in comparison to known platforms while maintaining a sufficiently large effective volume. It is considered advantageous to have a reduction between 15 and 35 percent, and especially favorable if it is in the range of 20 to 30 percent. A 30 percent reduction in length will result, for instance, from a decrease in platform length from 10 mm to 7 mm.
Another means of forming the structure stabilization device, while maintaining the length of the trial platform, is by increasing the rim thickness of the platform. Otherwise the other geometric dimensions of the trial platform can be maintained unchanged in comparison to a known trial platform.
Even a great rim thickness results in a low decrease in the effective volume which in no way affects the use of the trial platform for conducting corresponding measurements.
It was observed that increases in the rim thickness ranging from 10 to 50 percent in comparison to known platforms are sufficient. A thickening of 25 to 45 percent is preferable, and a thickening of 30 to 40 percent is particularly advantageous. An increase in rim thickness of 0.65 mm produces a thickening of the rim by about 38 percent, for instance, in comparison to a rim thickness of 0.47 mm in a known trial platform.
An additional means of configuring the geometric structure stabilization device is through an increase in the height of the rim. Once again the other geometric dimensions of the trial platform can remain unchanged in comparison to known trial platforms. In increasing the height of the rim, care must be taken that it is not so great as to influence the irradiated electromagnetic waves that are to be absorbed by the atomized trial. This can occur, for instance, through a more precise arrangement of the heat duct and/or trial platform relative to the direction of radiation of the electromagnetic waves.
It has been shown that it is possible to increase the rim height of the trial platform by 40 to 240 percent in comparison to known trial platforms. An increase of 80 to 200 percent is preferable, and of 100 to 150 percent is particularly advantageous. For instance, a 125 percent increase of rim height has been achieved with a rim height of 0.18 mm as opposed to a rim height of 0.08 mm in a trial platform that is in common use.
In relation to the aforementioned concrete values, it should be pointed out that they are provided only by way of example. A corresponding geometric structure stabilization device can also be used in trial platforms in current use, which have other concrete values for length, rim thickness, and rim height.
In order to stabilize the inventive structure still further, the geometric structure stabilization device can simultaneously include a reduction of the platform length and/or an increase of the rim thickness and/or an increase of the rim height.
Since the trial platform as a rule always includes a certain pretensioning, there can be an additional advantageous impact on this pretensioning if an increase in rim thickness and/or in the rim height is arranged, for instance, at just one end of the platform. In this respect, it is important to remember that it is possible, for instance, that an increase in rim thickness could occur at one end of he platform and an increase in rim height at the other end, or vice versa.
It is possible, in addition, that an increase in both rim thickness and rim height could occur at one end, whereas at the other end of the platform there is only an increase in rim height or in rim thickness. Other combinations of corresponding geometric structure stabilization devices are obvious.